Drill string shock absorbers



y 14, 1968 A. H. SALVATORI ETAL 3,383,126

DRILL STRING SHOCK ABSORBERS Filed Jan. 18, 1967 Mai Ea, 16; 3b.

fix I 8 Z 10/ INVENTORS,

ALsEQrHf sAzwn-o/qr, 45 LEO A. 134/206 United States Patent 3,383,126 DRILL STRING SHOCK ABSORBERS Albert H. Salvatori, 4 Queens Gate Place, London SW. 7,

England, and Leo A. Tairov, 1402 N. Benton Way, Los Angeles, Calif. 90026 Continuation-impart of application Ser. No. 371,219,

May 29, 1964. This application Jan. 18, 1967, Ser.

1 Claim. (Cl. 285-302) ABSTRACT OF THE DISCLOSURE This invention relates to a drill string shock absorber adapted to be inserted into a rotary drill string to absorb vibrational and shock forces therein. The shock absorber includes telescopically related parts which are separated and isolated one from the other by a mass of compressible wire material.

This application is a continuation-in-part of application Ser. No. 371,219, filed May 29, 1964, and now abandoned.

This invention relates to well drilling equipment and more particularly to a drill string shock absorber for use in a rotary well drilling string.

In the rotary method of well drilling it has become common practice to employ a drill collar section above the bit with drill pipe extending upward from the drill collar section. The drill collar section supplies as much weight as possible directly above the bit, such that the compressive force necessary on the bit is exerted by the drill collar section while the drill pipe portion of the string remains in tension. However, a rotary drill bit in meeting various earth strata continuously subjects the drill string to shock and vibration. The drill collar removes much of the vibrational and shock forces but a substantial amount of bouncing of the bit on the bottom of the hole can still result under various circumstances. This is especially true when resonance is induced which can cause severe vibration even above the rotary table. Accordingly under certain circumstances severe shocks and vibrations are imparted from the drill bit to the drill string whether or not a drill collar section is employed.

The present invention provides for the absorption of vibrational and shock forces from the bit so that they will not be relayed through the drill string. This shock absorber consists of a body portion, a mandrel, and a compressible resilient member positioned longitudinally between the mandrel and the body portion. Shock and vibrational forces are transmitted from the mandrel to the compressible material where they are damped out and are not further transmitted upwardly through the body portion to the drill string. In US. Letters Patent No. 3,225,566, filed Oct. 7, 1963, by Clarence H. Leathers for Drill String Shock Absorber, and issued Dec. 28, 1965, and assigned to the assignee of the present application, a shock absorber of the type which is the subject of the present invention is described which utilizes a compressible fluid in a closed chamber positioned between the mandrel and the body portion of the shock absorber. The fluid is sufficiently compressible to absorb the shock and vibration forces while transmitting the drilling force to the drill bit. Although suitable for most applications the present invention constitutes an improvement over the prior filed application in that it utilizes a compressible material which is not fluid and which eliminates the diflicult sealing problem encountered when a compressible fluid is to be contained in a closed chamber under high pressure.

An object of the present invention is the provision of an improved drill string shock absorber.

Another object of the present invention is the provision of a drill string shock absorber for damping out vibrational shock or intermittent forces which otherwise may have harmful elfects on the drill string.

Another object of the present invention is the provision of a drill string shock absorber which is elficient and has a longer useful life than shock absorbers heretofore known to the art.

It is another object of the present invention to provide an improvement drill string shock absorber which requires no special drilling procedure for its eflicient operation.

Yet a further object of the present invention is to provide such a shock absorber in which sealing and manufacturing problems are minimized.

Summary of the invention The present invention provides a drill string shock absorber adapted to be inserted into a rotary drill string. The shock absorber in accordance with the present invention includes a body portion defining a cylindrical inner chamber and a mandrel portion telescopically positioned in the chamber. The body and mandrel portions are adapted to be connected to other drill string apparatus for insertion into the drill string. The mandrel and body telescopically connected define by their transverse surfaces a generally closed axially extending variable volume in which is positioned a mass of resilient compressible wire material substantially filling the volume to absorb shock and vibrational forces transmitted axially along the drill string.

The novel features which are believed to be characteristic of the invention both as to its organization and method of operation together with further objects and advantages thereof will be better understood from the following description considered in connection with the accompanying drawing in which 'a presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description only, and is not intended as a definition of the limits of the invention.

In the drawings:

FIGURE 1 is a fragmentary vertical sectional view through the earth showing a device installated in a drilling string within a well and showing the preferred relationship of the installed device to the drill bit;

FIGURES 2a and 2b are enlarged half sectional views in elevation;

FIGURE 3 is a transverse view taken along line 3-3 of FIGURE 2; and

FIGURE 4 is a view of the resilient member utilized in the presently preferred embodiment of the present invention.

Referring now to the drawing, there is shown in FIG- URE 1 a typical mode of operation of the shock absorber in accordance with the present invention. The shock absorber 10 is shown disposed between a drill collar section 12 of the drill string 14 and the usual rotary bit 16 in a well 18. The drill collar 12 is of sufficient weight to provide the necessary compressive force on the bit during drilling operations. The drill collar of the drilling string is typically one or more sectionsof steel tubing ten feet or more in length. The drill collar is provided with a fluid conducting bore but is of considerably greater wall thickness than the drill pipe. Thus, a drill collar provides additional weight and rigidity in the drilling assembly immediately above the drilling tool. As an illustration, such a drill collar section in drilling a 12% inch hole, for example, typically may weigh on the order of 100,000 pounds and it is primarily this weight that is exerted on the bit at the bottom of the hole during drilling operations. 'The drill string 14 is supported under tension in the usual manner by suspension from a rotary table above the surface 22 of the earth.

In the FIGURES 2a and 2b, there is shown a presently preferred embodiment of the shock absorber of the present invention which comprises in general a body A and a mandrel B telescopically mateable therein for axial movement of the body A and mandrel B relative one to the other. The body A is of elongate cylindrical configuration having an outside surface 23 of substantially constant diameter approximately equal to the outside diameter of the drill collar 12 and substantially less than the diameter 18 of the well being drilled. At the upper end of the body A there is provided a male-threaded connecting end 24 of the conventional type for a connection to the lower end of the adjacent drill collar or drill string component. Although the body A can be formed as an integral unit, for ease of manufacture it is constructed by division into an upper portion 26 and a lower portion 30 in the presently preferred embodiment. The upper portion 26 and the lower portion 30 are threadably engaged by mating threads 25 and appropriate sealing means 27. The body A defines by its internal surface 32 an upper cylindrical bore 38 and by its lower internal surface 34 a lower cylindrical bore 42. Although intermediate diameters to accommodate thread formation and assembly may be necessary the cylindrical bores 38 and 42 are those that determine the operation of the device as will become more apparent thereinafter. The upper cylindrical bore extends from the upper end of the body in communication with the bore 40 through the drill collars and remainder of the drill string for circulation of drilling fluid. The length of the bore 38 is dependent upon the length of movement of the mandrel as discussed more fully hereinafter. The lower cylinder 42 defined by the wall 34 is of substantially greater inside diameter, being limited only by the necessary wall thickness of the body at that portion defining the lower cylinder 42. The lower cylinder 42 extends from a point proximate the upper end of the lower portion 30 of the body to the lower end 44 thereof. Thus, the lower end of the body is open with an inside wall 34 extending upwardly to a point just below the connection of the lower portion 30 of the body to the upper portion 26 thereof. The cylinder walls 32 and 34 then define a shoulder 43 therebetween. Illustrative of the relative diameters, in a typical embodiment of a shock absorber of one size the bore 38 defined by upper cylinder wall 32 is approximately three inches in diameter while the lower cylinder 42 is approximately eight inches in inside diameter. A region of decreased wall thickness and spline grooves are provided in the body extending upwardly from the lower end thereof and is described hereinafter.

Through the wall of the body there are provided a series of longitudinally spaced openings or ports 46 for inserting fluid into the shock absorber and checking the level thereof as discussed hereinafter.

A removable retaining ring 50 is positioned in an annular groove 52 in the cylinder wall 34 proximate the lower end 44 of the body.

Removal of the retaining ring 50 allows assembly of the mandrel B into the body and the ring 50 when positioned in groove 52 prevents disassembly and furnishes a stop surface 56 to limit the downward movement of the mandrel in the body as will become apparent hereinafter. i

The mandrel B as shown in FIGURE 2 is an elongate member having a bore 58 of substantially constant inside diameter extending throughout the length of the mandrel, which bore is co-extensive with the bore 40 through the drill string when the mandrel is assembled within the body as shown in FIGURE 2. The mandrel is adapted to be longitudinally slidably movable within the body portion of the shock absorber and to define an annular chamber 69 between the exterior surface of the mandrel and the interior wall of the body. For ease of manufacture the mandrel is again constructed in two parts which are threadably engaged by threads 62, that part of the mandrel above the threads being referred to herein as the upper portion or tubular portion 64 of the mandrel and that beneath the threads being referred to as the lower portion 66 of the mandrel. The tubular portion 64 of the mandrel has an outside diameter substantially less than the inside diameter of the bore 38 in the upper portion of the body A and is adapted to be slidably movable with respect thereto. As shown particularly in FIGURE 2a sealing means are provided between the outer surface of the tubular portion and the cylinder wall 32 of the body to provide fluid sealing therebetween. Specifi cally, a seal 49 is provided in an annular groove defined between the upper and lower sections of the body portion. A back-up ring 53 is positioned above the seal in the groove. The seal is so shaped as to define a lip preventing the ingress of drilling fluid to the chamber 60.

The lower mandrel portion 66 has a maximum outside diameter substantially equal to, but less than, the diameter of the cylinder Wall 34 such that it is slidably mateable therewith. At the lower end of the lower mandrel portion 66 there is provided a threaded joint 72 for connection of the bit 16 or other element in the drilling string. As shown in FIGURES 2b and 3 proximate the upper end of the lower portion 66 of the mandrel there are provided a series of circumferentially spaced longitudinally extending grooves 74 in the outer surface thereof. At a corresponding longitudinal position along the cylinder wall 34 of the body B there is provided an inwardly extending annular protrusion 76 in which circumferentially spaced longitudinally extending grooves 78 are formed. The grooves 78 in the internal wall of the body are spaced in mateable relationship with the grooves 74 in the mandrel such that splines 80 can be inserted therein as shown in FIGURES 2b and 3, to allow longitudinal movement of the mandrel and body while preventing rotational movement therebetween. These splines are thus drive splines which cause the mandrel to be rotated when the body is rotated.

As shown in FIGURE 2b the mandrel increases to its maximum diameter beneath the spline portion and in this region of maximum diameter there is provided a region of decreased wall thickness in the body portion 30. Between the outer surface of the mandrel portion 66 and the internal wall 34 of the body portion 30 there is provided a sealing assembly 79. In this embodiment the sealing assembly includes a ring-like member 82 extending circumferentially around the mandrel. The ring member 82 is afiixed to the mandrel along its mid-portion and extends outwardly from the mandrel above and below the midpoint. A first sealing ring 84 in sealing engagement with the mandrel surface is positioned above the mid-point of the ring while a second sealing ring 85 is positioned below the mid-point in sealing engagement with the body wall 34.

From the foregoing it will be seen that the mandrel and body define therebetween a cavity 60 which is annular in configuration and extends from the upper shoulder 43 to the lower shoulder 100, which shoulder is defined by the upper end of the lower mandrel portion 66.

In this cavity designated generally as 60 there is positioned a resilient compressible member or members. In the presently preferred embodiment a plurality of members, one of which is shown in FIGURE 4, is utilized. The compressible resilient members are such that they will not be compressed under the normal loads imposed on their volume to an extent suflicient to prevent isolation of the body from the mandrel. Conversely, the plurality of members must be sufliciently compressible as to provide :a damping action under the loads imposed. In this embodiment a toroidal shaped member formed of knitted wire is utilized. Such members are commercially available and are resilient vibration and shock isolators made of knitted wire which is stainless steel or similar material 0.001 to 0.020 inch in diameter.

The resilient knitted wire members 101 can be designed to fail at predetermined compressive loads. The wire elements which comprise members 101 can be of greater or smaller diameter as desired and can be manufactured (by a knitting process) to produce wire members 101. Thus, the multiple wire elements in the knitted wire members are of predetermined and different thicknesses and can be made to exceed their elastic limits at different times under varying loading conditions. By utilizing this design it is possblie to provide a plurality of shock absorbing elements which have different moduli of elasticity and consequently different compressive fail points. Therefore, under any given loading conditions the shock absorbing elements do not all fail at once but provide a non-linear response to higher deflection due to increased load. This prevents shock and vibration at the drilling bit from reaching the drill string through the collapsed knitted wire members.

In use, a predetermined number of knitted wire members 101 having a high modulus of elasticity (and therefore high compressive fail point) can be stacked in chamber 60. A second predetermined number of elements 101 having a lower modulus of elasticity can then also be stacked in chamber 60 to fill the cavity. With this arrangement the shock absorbing elements will not fail simultav neously but will fail incrementally under increasing load conditions.

It should also be noted that in the embodiment of the present invention in which the knitted wire members 101 are manufactured to the same specifications (with no designed strength diflerences) the fail points of the various shock absorbing elements will necessarily be at different loads due to small materials differences and differences inherent in the manufacturing process. The magnitude of the differences in the ultimate compressive strengths for the knitted Wire members due to manufacturing parameters is largely unpredictable for each individual element but covers a well defined range when all the elements are assembled as in chamber 60.

The members are preformed in toroidal configuration with an inside diameter greater than the outside diameter of the upper portion 64 of the mandrel and an outside diameter substantially equal to the inside diameter 34 of the body. The members can thus be inserted over the tubular portion of the mandrel into engagement with the shoulder 100 and stacked to a depth at which they are in contact with the shoulder 43 of the body in the normal, or relaxed, condition of the assembled shock absorber apparatus. The knitted wire member-s are such that they are compressible under load but will take no permanent set and will, due to their resilience, resume their normal unloaded thickness. When the necessary compressibility of the apparatus does not require that the entire volume of the chamber 60 be filled with members 101, spacers can be utilized such as shown at 102.

The knitted wire members 101 are, of course, comprised of intertwined wires with voids between which allow the compressibility. In the presently preferred embodiment oil is introduced into the chamber 60 in sufficient quantity to provide lubrication between the splined body and mandrel but not in suflicient volume as to be compressed or to resist the longitudinal movement of the body and mandrel relative to one another as discussed m'ore fully hereinafter. The lubricating oil or fluid will, in large measure, be contained in the voids of the members. The compressibility of the members 101 and ,connected to the drill collar section 12 at the upper end 24 of the body shock absorber with no upward force on the bit, members 101 will remain in the fully expanded condition as shown in FIGURE 2 with the stop surface 98 of the mandrel in bearing contact with the retaining ring positioned in the body after assembly. The shock absorber will remain in this condition during lowering into the well and until the bit rests on the bottom of the hole. As the weight of the drill collar is lowered onto the bit the mandrel is urged upwardly into the body. At this point it can be seen that as the stop surface 98 is moved upwardly from the retaining ring 50 there is no longitudinal connection between the bit and the drill string except through the members 10 1 occupying the chamber 60. That is, the bit is connected longitudinally only to the mandrel, while the drill string is connected longitudinally only to the body and the mandrel and body are connected longitudinally only through the members in the cavity 60. Accordingly, as the weight of the drill collars is lowered onto the bit all of the downward force is exerted against the members by the effective area of the downwardly facing shoulder 43. These forces are transmitted to the mandrel by the force of the members acting against the upward facing transverse shoulder 100 of the mandrel extending from the diameter of bore 32 to that of cylinder wall 34. Accordingly, the transverse mandrel surface 100 acts as a piston face of the mandrel movable within the cylinder. Thus, as the weight of the drill collar comes to rest on the bit the members within the cavity are compressed by that amount of force. For example, under a drill collar load of 100,000 pounds the members are compressed sufliciently to allow the mandrel to move upwardly by approximately 1%" in the illustrative embodiment described.

From this balanced position under load, the mandrel is then free to move upwardly or downwardly relative to the body against the compressible members when shock forces, vibrations, or other intermittent forces are exerted on the bit. The compressibility of the members prevents such intermittent forces from being transmitted to th body A and thus to the drill string by absorbing such forces due to their compressibility. In effect the members act in a manner similar to a spring in absorbing and damping out shocks and vibrations transmitted to it.

Although knitted wire members have been shown and described in this embodiment other members formed of knitted plastic or similar resilient compressible material can be utilized.

The present invention thus provides an improved drill string shock absorber which is simple and eflicient in operation, does not require hydraulic horsepower for its operation, is self-contained and cap-able of long periods of operation. Diflicult sealing problems are eliminated.

What is claimed is:

1. A drill string shock absorber comprising:

a generally enlongate cylindrical shock absorber body having a cylindrical chamber therein;

a mandrel telescopically positioned in said body chamber with the outer surface of said mandrel spaced inwardly from the inner surface of said body;

means on said body and mandrel for connection to other drill string apparatus;

means for rotationally drivingly connecting said body to said mandrel;

said body and said mandrel having axially spaced transverse surfaces extending between the inner surface of said body and the outer surface of said mandrel, said inner, outer and transverse surfaces defining a generally closed axially extending variable volume cell therebetween;

a mass of resilient compressible wire material substantially filling said cell and subjected to compressive loading absorbing shock and vibrational forces transmitted axially of said body and mandrel when 'said body and mandrel are axially moved toward each other thereby decreasing the volume of the said variable volume cell wherein said mass of resilient compressible Wire material comprises a plurality of knitted wire members said knitted wire members having different fail points under com- 'pressive loading.

References Cited UNITED STATES PATENTS Griepenstr-oh 285-302 X Williams 28594 X Brimhall 280-436 Hartwell.

Warren 6423 Blair et al 6423 Keetch.

Leathers.

EDWARD C. ALLEN, Primary Examiner.

CARL W. TOML'IN, Examiner.

15 'D. W. AROLA, Assistant Examiner. 

